Bright acid copper plating



United State Patent BRIGHT ACID COPPER PLATING Frank Passal, Detroit, Mich., assignor, by mesne assignments, to Metal & Thermit Corporation, New York, N. Y., a corporation of New Jersey No Drawing. Application October 31, 1952, Serial No. 318,070

14 Claims. (Cl. 204-52) This invention relates to the electroplating of bright copper, and more particularly to addition agents for bright acid copper plating baths.

The invention provides a copper sulphate-sulphuric acid bath for electroplating bright copper having new and advantageous combinations of organic addition agents, which combinations have a brightening action, and further provides a process making use of such a bath.

According to the invention, a novel and improved combination of addition agents comprises Z-mercaptobenzimidazole (hereinafter designated in abbreviated form as Z-mbi) or a derivative of the same, and thiourea of an acyl derivative of thiourea. In general, useful derivatives of 2-rnbi comprise 2-m-bi substituted in the 6-membered ring by a radical linked to the Z-mbi through a nitrogen atom, that is, amino and substituted amino radicals. One or more of such radicals may be substituted in the Z-mbi. The substituted amino radicals include sulfanilamido, p-toluene sulfanilamido, and acylamido radicals; in the acylamido group the acyl moiety preferably has a small number of carbon atoms, say up to six to ten, for example: acetamido, propionamido, butyramido, benzamido, etc. Other substituted amino radicals are the monoalkyl amino radicals, NHR, wherein the alkyl group, R, preferably has 1 to 6 carbon atoms; and the dialkyl amino radicals, -NRR', wherein the alkyl groups R,R preferably have 1 to 2 carbon atoms. Specific examples of the foregoing derivatives are -sulfanilamido-2-mbi, 4-para-toluene sul-fanilamido- Z-mbi, 6-acetamido-2-mbi, 6-propionamido-2-mbi, 5- butyramido-Z-mbi, S benzamido-Z-mbi, G-(N-methyla-mino)-2-mbi, and 6-(N,N-diethylamino)2mbi. The acyl derivatives of thiourea are those in which the acyl group has a small number of carbon atoms, suitable examples being acetylthiourea, propionylthiourea, and benzoylthiourea. Preferred combinations of addition agents are S-amino-Z-mbi and thiourea, also 4-arnino-2-mbi and thiourea, and 2-mbi and thiourea.

Wetting agents of the kind generally used in acidic electroplating baths, including sulfated fatty acid alcohols like sodium lauryl sulphate (Duponol PC), sodium cetyl sulphate, sodium myristyl sulphate, or mixtures thereof, may be usefully employed in some cases,

and it may be advantageous to employ with them suitable foam-reduoing agents like trioctylphosphate and octyl alcohol.

The concentration of the thiourea type agent in the copper plating electrolyte may vary from about 0.0025 to 0.03 g./l. The concentration of the 2-mbi type agent is within the same range as the concentration of the thiourea type agent, and what is surprising, may vary relatively to the latter concentration within said range. The fact that these agents may vary relatively to each other means that, notwithstanding the probability that the agents are consumed at unequal rates, the bath will not tend to become unbalanced, particularly during prolonged plating runs. A preferred concentration for each 2,758,076 Patented Aug. -7, 1956 type of agent is 0.01 g./l. Concentrations above 0.03 g./l., while effective, do not justify the added cost of the agents in view of the satisfactory brightening action obtainable at lower concentrations. Below a concentration of 0.0025 g./l., the combination of agents only slightly enhances brightness; however, at concentrations below 0.0025 g./l., say down to 0.0005 g./l., the agents may be used to secure grain refinement in the deposit, improved leveling, softness, and better buifability. The concentration of the other constituents of the bath may be varied to meet special requirements, as is conventional.

It is to be understood in this connection that conventional acid copper baths and operating conditions are applicable. Thus, the copper sulphate may range from 50 to 300 g./l., preferably from 200 to 300 g./l., and the sulphuric acid from 5 to 100 g./l., preferably from 50 to 70 g./l. The bath temperature may extend from room temperature to 130 F. and the current density from 10 to amperes per square foot.

The invention may be illustrated by the following examples:

Example 1 A solution was made up containing 250 g./l. of copper sulphate and 60 g./l. of sulphuric acid. Using this solution as the basic electrolyte composition, 2-mbi and thiourea were added, each in a concentration of 0.0025 g./l. Plating was then carried out with this bath at about 75 F. with air agitation of the electrolyte. The concentrations of the Z-mbi and thiourea were then increased equally from time to time, and the plating ac tion of the bath was studied at each new concentration until a final concentration of 0.03 g./l. was reached. It was found that highly lustrous deposits without striations and exhibiting good leveling could be obtained throughout these ranges of concentration and over a wide current density range, which in these runs extended from about 10 to 60 amps. per sq. ft.

Example 2 A solution was made up containing 250 g./l. of copper sulphate and 60 g./l. of sulphuric acid. To it were added 0.01 g./l. of S-amino-Z-mbi and 0.01 g./l. of thiourea. This bath was operated with air agitation at temperatures up to 120 F. and current densities up to amps. per sq. ft., and under these conditions it gave very bright, smooth, fine-grained, soft deposits which had exceptionally good leveling action.

Cathode or air agitation may be employed, the degree to be deter-mined by the type of work being plated and the operating current density. Good results may be obtained without any solution or cathode agitation by regulating the current density and the temperature within the above-noted ranges.

The thiourea type compound and the 2-mbi type compound, when used in combination, provide a bright acid copper plating bath superior to present commercial bright acid copper plating baths. The compounds have good stability, no evidence having been found that they accumulate harmful decomposition products. The rate of their consumption is low. The process is characterized by a wide and easily maintained bright plate current density range. The copper deposits are uniform, lustrous and easily buffed, and they exhibit good leveling.

Although the invention has been illustrated by selected embodiments, it will be appreciated that these are illustrative and that the invention is capable of obvious variations.

In the light of the foregoing description, the following is claimed:

1. An aqueous acid bath solution for bright copper plating containing copper sulfate as the source of the 3 copper, sulfuric acid, about 0.0005 to about 0.03 g./l. of a first compound selected from the class consisting of 2- mercapto-benzimidazole and derivatives of 2-mercaptobenzimidazole having in the 6-membered ring thereof a radical selected from the class consisting of amino and substituted amino radicals, and about 0.0005 to about 0.03 g./l. of a second compound selected from the class consisting of thiourea and acyl derivatives of thiourea.

2. An aqueous bath solution according to claim 1 in which said second compound is thiourea.

3. An aqueous bath solution according to claim 1 in which said second compound is an acyl derivative of thiourea.

4. An aqueous bath solution according to claim 1 in which said first compound is 2-mercapto-benzimidazole.

5. An aqueous bath solution according to claim 1 in which said first compound is Z-mercapto-benzimidazolc having an amino radical substituted therein.

6. An aqueous bath solution according to claim 1 in which said first compound is Z-mercapto-benzimidazole having a substituted amino radical substituted therein.

7. An aqueous bath solution according to claim I in which said first compound is 2 mercapto-benzimidazo]e and said second compound is thiourea.

8. An aqueous bath solution according to claim 1 in which said first compound is 2-mercapto-benzimidazole and said second compound is acetylthiourea.

9. An aqueous bath solution according to claim 1 in which said first compound is Z-mercapto-benzimidazole having an amino radical substituted therein and said second compound is thiourea.

10. An aqueous bath solution according to claim 1 in which said first compound is Z-mercapto-benzimidiazole having an amino radical substituted therein and said second compound is acetylthiourea.

11. An aqueous bath solution according to claim 1 in which said first compound is Z-mercapto-benzimidiazole having a substituted amino radical substituted therein and said second compound is thiourea.

12. An aqueous bath solution according to claim 9 in which the said first compound is 5-amino-2-mercaptobenzimidiazole and the said second compound is thiourea.

13. An aqueous acid bath solution for bright copper plating containing copper sulfate as the source of the copper, sulfuric acid, a first compound selected from the class consisting of Z-mercapto-benzimidiazole and derivatives of 2-mercapto-benzimidazo1e having in the 6-membered ring thereof a radical selected from the class consisting of amino and substituted amino radicals, and a second compound selected from the class consisting of thiourea and acyl derivatives of thiourea, each of said compounds being present in a concentration of 0.0025 to 0.03 g./l.

14. A process for electrodepositing bright copper which comprises electrodepositing said copper from an aqueous acid bath solution containing copper sulfate as the source of the copper and sulfuric acid, and as addition agents, a first compound selected from the class consisting of 2-*nercapto-benzimidazole and derivatives of Z-mercapto-benzimidazole having in the 6-membered ring thereof a radical selected from the class consisting of amino and substituted amino radicals, and a second compound selected from the class consisting of thiourea and acyl derivatives of thiourea, each of said compounds being present in a concentration of 0.0005 to 0.03 g./l.

References Cited in the file of this patent UNITED STATES PATENTS 2,391,289 Beaver Dec. 18, 1945 2,609,339 Passal Sept. 2, 1952 2,700,020 Pierce Jan. 18, 1955 FOREIGN PATENTS 461,186 Canada Nov. 22, 1949 

1. AN AQUEOUS ACID BATH SOLUTION FOR BRIGHT COPPER PLATING CONTAINING COPPER SULFATE AS THE SOURCE OF THE COPPER, SULFURIC ACID, ABOUT 0.0005 TO ABOUT 0.03 G./1. OF A FIRST COMPOUND SELECTED FROM THE CLASS CONSISTING OF 2MERCAPTO-BEZIMIDAZOLE AND DERIVATIVES OF 2-MERCAPTOBENZIMIDAZOLE HAVING IN THE 6-MEMBERED RING THEREOF A RADICAL SELECTED FROM THE CLASS CONSISTING OF AMINO AND SUBSTITUTED AMINO RADICALS, AND ABOUT 0.0005 TO ABOUT 0.03 G./1. OF A SECOND COMPOUND SELECTED FROM THE CLASS CONSISTING OF THIOUREA AND ACYL DERIVATIVES OF THIOUREA. 